Injection unit with a rotating valve for processing meltable materials

ABSTRACT

The invention is based on an injection unit for the processing of fusible materials, for example thermoplastics, ceramic or metallic compositions or the like, in which at least two melt streams are fed via a channel system to one or more mould cavities in a sequence which changes with time.  
     In accordance with the invention, only one rotating valve element is provided for each channel system which leads to the mould cavity (cavities) and consists of at least two feed channels ( 6; 7 ). The valve element consists of a hollow spindle ( 11 ), which is connected to the pressure channel ( 20 ) of the melt and has, in the plane of the feed channels ( 6; 7 ) leading to the mould cavity (cavities), at least one distribution channel ( 21 ) which runs radially outwards and is likewise connected to the pressure channel ( 20 ).

PRIOR ART

The invention is based on an injection unit for plants for theprocessing of fusible materials, for example thermoplastics, ceramic ormetallic compositions or the like, as defined in the main claim.Processing plants of this type are known, for example, asinjection-moulding or alternatively extrusion plants for the area ofplastics processing plants and as injection-moulding plants for ceramicand metallic compositions. In this principle of moulding production,mould cavities formed correspondingly to the mouldings to be producedare filled with melt. The injection unit here is part of the hotchannel, through which the melt is conveyed at low or high pressure atthe processing temperature necessary for the particular substance, andenters the mould cavity via nozzles. In order to ensure high productquality, i.e. both adequate strength throughout the moulding and opticaluniformity, it is necessary to achieve intimate mixing of the meltstreams at the flow lines, i.e. the points in the moulding where thepreviously separate melt streams meet one another again. To this end, itis already known to set the individual melt strands in vibration orpulsation, at least in sections, causing the melts to penetrate throughin the region of the flow lines owing to the vibration differences andthe flow lines to undergo intensive bonding to one another at the jointof the melt strands (DE 100 52 841 A1). This publication also describesa plastics processing plant with a plastics injection-moulding machine,an injection-moulding tool having a cavity for the injection mould andat least two injection valves, each with a control mechanism, forcorresponding injection nozzles opening into the cavity. The valves canbe opened or closed by the control mechanism, independently of theinjection pressure, with the control mechanism of the individual valvesbeing synchronised with one another. The simplest form of valve is avalve needle having an inclined groove arranged on its outer surface.However, the use, likewise described, of rotary slides with rollerbearings and T-shaped control channels is more favourable from afunctional point of view. The disadvantage of these solutions consistsin the relatively high complexity required by this injection unit. Afterall, pressures of up to 3000 bar prevail in the injection unit. Therotating valve needles or rotary slides must be sealed off from thecasing, which in turn makes the injection unit more expensive. Inaddition, there is the complexity for synchronisation, which in allcases requires a gearbox. Also disadvantageous is the space requirementfor this design. The spatial capacity in the hot channel is limited.Finally, mention should be made of the complexity for thermalinsulation, which in each case has to be operated for two rotatingparts.

THE INVENTION AND ITS ADVANTAGES

The injection unit according to the invention with the characterisingfeatures of the main claim reduces the complexity for sealing, thermalinsulation and drive on a channel system supplying only one rotatingcomponent per mould cavity. In addition, synchronisation of the rotationof two valve needles or rotary slides which supply the same mould cavitywith melt is unnecessary. This has been achieved by a design in whichthe melt enters a rotating hollow spindle directly and passes from thisthrough at least one distribution channel which runs radially outwards,to the nozzles opening into the mould cavity. This means that only onerotating valve element, i.e. a hollow spindle, is provided for each ofthe associated melt strands, i.e. for the melt strands which form achannel system and are combined again in one and the same mould cavity.The hollow spindle thus has two jobs, namely transportation of the meltflow to at least two channels, and interruption of the melt flow inorder to generate the pulsation. It is of course also conceivable for aplurality of channel systems to be supplied by one hollow spindle. It isunimportant here whether the channel systems supply one or more mouldcavities with melt.

According to an advantageous embodiment of the invention, the hollowspindle has two distribution channels which run radially outwards andare not arranged at the same angle to one another as the feed channelsintended to supply them with melt. If, for example, the two channels arelocated precisely opposite one another, the angle between the twodistribution channels must not be 180° in order that the filling of thetwo channels takes place successively in terms of time. The arrangementof more than one distribution channel has the advantage that thepulsation frequently can be increased without changing the rotationalspeed of the hollow spindle.

According to a further advantageous embodiment of the invention, thedistribution channels are arranged at levels of the hollow spindle whichlie one above the other, even if the channels are arranged one on top ofthe other.

Further advantages and advantageous embodiments of the invention arerevealed by the following example description, the drawing and theclaims.

DRAWING

An illustrative embodiment of the invention is shown in the drawing andis described in greater detail below. The figure shows a cross sectionthrough an injection unit in the reverse installation position, whichserves on the nozzle side as platen for an injection-moulding machine.It consists of a platen 1 and an intermediate plate 2, which are firmlyconnected to one another by means of guide columns 3 and cap screws 4.The injection unit is thermally insulated from the adjacent parts of theinjection-moulding machine by means of an insulation plate 5. In thepresent depiction, the mould cavity (not depicted in greater detail),into which two feed channels 6 and 7 open, follows below theintermediate plate 2. A heating block 8, which is held at the meltingpoint by heating cartridges 9 and 10, is located in the interior of theintermediate plate 2. The central constituent of the injection unit is ahollow spindle 11, which is guided in the heating block 8 by means of awear sleeve 12 and a bearing ring 13. In the region of the platen 1, achain wheel 14 is connected in a rotationally fixed manner to the hollowspindle 11 via a tongue-and-groove joint. The bearing of hollow spindle11 and chain wheel 14 in the platen 1 takes place by means of a bearingplate 15 and groove ball bearings 16. The hollow spindle 11 has anadditional guide in the transition region from the platen 1 to theintermediate plate 2 through a guide sleeve 17, a support ring 18 and awear ring 19. The cavity of the hollow spindle 11 is connected to thepressure channel of the injection-moulding machine so that the meltenters the latter. In the present sectional depiction, this is indicatedby the pressure channel 20, which, after a short axial guide, becomes aradial distribution channel 21.

The mode of action of the invention will be described in greater detailbelow. The chain wheel 14 and thus also the hollow spindle 11 is, in thepresent example, driven by means of a chain (not shown) of a gear motor(likewise not shown). The distribution channel 21 of the hollow spindle11 thus alternately connects the two feed channels 6 and 7 to thepressure channel 20, so that the melt stream, divided into two partialmelt streams, enters the mould cavity in a pulsed manner. The hollowspindle 11 accordingly has a double function, namely that ofdistribution of the melt over at least two feed channels and generationof the pulsation. In the present example, the hollow spindle 11 has onlyone radial distribution channel 21, i.e. during a rotation of the hollowspindle 11, each of the feed channels 6 and 7 is also only connected tothe pressure channel 20 once. The pulsation frequency of a feed channel6; 7 accordingly corresponds to the rotational speed of the hollowspindle 11, with the pressure pulses in each case being phase-shifted by180°. If more than one distribution channel 21 is provided in a plane,these must always be at a different angle to one another than the feedchannels 6; 7 located in this plane, i.e. it must be ensured that,whenever a feed channel 6; 7 is just connected to the pressure channel20, the other is closed by the envelope of the hollow spindle 11.

All features represented in the description, the following claims andthe drawing can be essential to the invention, both individually and inany desired combination with one another.

List of Reference Numerals

-   1 platen-   2 intermediate plate-   3 guide columns-   4 cap screws-   5 insulation plate-   6 feed channel-   7 feed channel-   8 heating block-   9 heating cartridge-   10 heating cartridge-   11 hollow spindle-   12 wear sleeve-   13 bearing ring-   14 chain wheel-   15 bearing plate-   16 groove ball bearings-   17 guide sleeve-   18 support ring-   19 wear ring-   20 pressure channel-   21 distribution channel

1. Injection unit for the processing of fusible materials, in which atleast two melt streams are fed to one or more mould cavities via achannel system in a sequence which changes with time, with the change intime of the feed of the melt streams taking place through temporaryopening and closing of the feed channels (6; 7) leading to the mouldcavity (cavities), and, as means for temporary opening and closing ofrotating valve elements, the feed channels (6; 7) connect to thepressure channel (20) of the melt alternately one after the other,characterised in that only one valve element is provided for eachchannel system which leads to the mould cavity (cavities) and consistsof at least two feed channels (6; 7), and the valve element consists ofa hollow spindle (11), which is connected to the pressure channel (20)of the melt and has, in the plane of the feed channels (6; 7) leading tothe mould cavity (cavities), at least one distribution channel (21)which runs radially outwards and is likewise connected to the pressurechannel (20).
 2. Injection unit according to claim 1, characterised inthat the hollow spindle (11) has two distribution channels (21) whichrun radially outwards and are not arranged at the same angle to oneanother as the feed channels (6; 7) intended to supply them with melt.3. Injection unit according to claim 2, characterised in that thedistribution channels (21) running radially outwards are in differentplanes in the hollow spindle (11).